Diphenylzinc-titanium tetrachloride polymerization initiator and process



applications but not for others.

Un ted Sta es Pate DIPHENYLZINC-TITANIUM TETRACHLORIDE I POLYMERIZATIONINITIATOR AND PROCESS No Drawing. Application February 9, 1956 SerialNo. 564,379

6 Claims. or. 260-935) This invention relates to new compositions ofmatter. More particularly, this invention is concerned with novelinitiators or activators for polymerizing olefins such as ethylene andpropylene. This invention is also con- 'cerned with novel processes ofproducing such initiators. Ethylene has been polymerized heretofore athigh temperatures and very high pressures with the aid of initiators ofthe free radical type. The polyethylenes resulting from high pressureprocesses have been suitable for some This is because it has beenparticularly diflicult to increase the rigidity and softening pointsofhigh pressure polyethylenes to levels necessary for the desiredapplications. There has been some success in producing polyethyleneswith the desired properties by employing higher pressures. Theseprocesses, however, utilize pressures considered above practical limitsfor convenient and economical commercial production. Somewhat betterresults have been attained by utilizing lower temperatures; However, thefree radi- Among these may be mentioned such initiators as the alkalimetal hydrides, Grignard reagents, triethyl aluminum and the activatedsupported transitional elements. However, the products of theseprocesses most often range from oils to low melting waxes. In thoseinstances where a satisfactorily high molecular weight polymer isobtained, the process is accompanied by pressures in excess of1000-p.s.i.g., temperatures above 100 C., or reaction times in excess offifteen hours.

By means of the present invention an initiator is provided which willpolymerize polyethylene to high molecular weights at atmosphericpressures and room temperatures and is flexible as to pressure andtemperature in that it will proceed satisfactorily at high or very lowtemperatures and at high or low pressures. According to the presentinvention, it has been found that the combination of diphenylzinc andtitanium tetrachloride gives a new composition of matter which is aninitiator of high activity for the polymerization of ethylene andpropylene. This is particularly surprising since neither diphenylzincnor titanium tetrachloride are effective as polymerization initiatorsfor olefins such as ethylene and propylene.

The initiator of this invention polymerizes ethylene and propylene atsurprisingly low temperatures and pressures to give products of highmolecular weights and high softening points. It is, therefore, possibleto form polyethylene and polypropylene resins without resorting to thehigher temperatures and pressures formerly used. A more suitable andconvenient process employing mild conditions is accordingly alsoprovided by this invention.

The initiator formed by contacting and reacting increased by the higherpressures.

, 2,911,399 Patented Nov. 3, 1959 diphenylzinc and titaniumtetrachloride is a novel composition that appears to be a complex ofpresently undetermined composition which is insoluble in most reactionmedia. Such complexes solvate with many media; however, the complex, aswell as solvated forms thereof, are useful initiators.

The initiators are conveniently prepared by intimately mixing adiphenylzinc and titanium tetrachloride in a liquid medium. Diphenylzincis very reactive but may be handled conveniently out of contact with airand water. It is preferred to employ as the medium an inert organicsolvent such as a saturated aliphatic or alicyclic hydrocarbon, anaromatic hydrocarbon or halogenated derivatives of such hydrocarbons.Preferred organic media are pentane, hexane, cyclohexane, isooctane,petroleum ether, benzene, toluene, monochlorobenzene and the like, andmixtures thereof.

To prepare the initiators, a ratio of about one molar equivalent ofdiphenylzinc to about 0.25 to 4.00 molar equivalents of titaniumtetrachloride is used. To prepare the preferred initiator, a ratio ofabout one mole of diphenylzinc to about one mole of titaniumtetrachloride is combined.

The order in which the reactants are added to the medium is generallynot critical. However, in certain situations it appears that solvationoccurs between the medium and one of the reactants which lowers itsreactivity. Therefore, the order of addition of the reactants should beadjusted appropriately. Thus, when toluene is the medium diphenylzinc ispreferably added first and then titanium tetrachloride to produce theinitiator.

After diphenylzinc and titanium tetrachloride have been united, reactiontakes place at room temperature although lower and higher temperaturesmay be used.

The initiator provided by this invention is particularly useful in thepolymerization of ethylene and propylene since they inducepolymerization, surprisingly, at relatively low temperatures andpressures and give products of high molecular weight and high softeningpoints. For best results, it is preferred to use the initiator soonafter preparation, viz., within an hour after preparation.

As previously indicated above, polymerization of ethylene and propyleneis effected with the initiator at low temperatures and pressures. Thepolymerization may be conveniently effected with the initiator attemperatures as low as that of liquid nitrogen and as high as thedecomposition temperature of the initiator which is about 300-500" C.However, excellent results may be attained with convenience at about 0C. to about C. and preferably at 20 C. to 60 C. The higher temperaturesapparently increase the rate of polymerization although the polymers soproduced may be of relatively lower molecular weight than those obtainedat lower temperatures.

Polymerization with the described initiator is achieved in this processover a wide pressure range from subatomspheric pressures to pressures ofabout 1000 p.s.i.g. and higher, such as pressures of 2000 atmospheres.However, lower pressures from about atmospheric to about 200 p.s.i.g.give generally preferred results and are most economically used. Ingeneral, the polymerization rate is However, the activity of theinitiator is such that there is not much reason in operating at thehigher pressures.

To effect the polymerization, the ethylene and/or propylene arecontacted with the initiator, preferably under liquid reactionconditions although vapor phase operations are within the scopecontemplated by this invention. Inert organic solvents such as saturatedaliphatic or alicyclic hydrocarbons, aromatic hydrocarbons orhalogenated derivatives of such hydrocarbons may be used as the reactionmedium. Preferred organic media are pentane,

toluene, monochlorobenzene and the like and mixtures thereof. Inaddition, by proper selection of temperatures and pressures liquidethylene and/ or propylene also may be used as the medium.

The amounts of initiator used to effect polymerization of ethylene andpropylene are not critical; all that is required is that an effectiveamount be used. The rate of polymerization as well as the molecularweight of the polymers can be varied by changing the ratio of initiatorto ethylene and propylene. Some loss of activity of the initiator may beexpected due to the presence of impurities that may be present in thereaction. It is, therefore, desirable to employ more than what may beconsidered to be trace amounts of the initiator.

The relationship of initiator to reaction medium is subject to widevariation. The larger amounts of initiator give a more rapidpolymerization than do lesser, minimum amounts. However, as little as.002 mole of initiator per 100 ml. of medium effect polymerization.

By the use of the described initiator, it has been found that highlypure ethylene and propylene need not be used to achieve satisfactorypolymerization. Ethylene and propylene of 95% purity containing loweralkanes, nitrogen, hydrogen and other inert materials are entirelysatisfactory at the low temperature-low pressure conditions which may beused with the initiator. This is opposite to conventional high pressureprocesses wherein high purity ethylene must be employed. The systemshould be maintained substantially free of water and oxygen, however,since these substances appear to affect the initiator adversely.

The rate of reaction is, of course, dependent on the other processconditions as already stated. The initiator is of such exceptionalactivity, however, that at 50 C. and 50 p.s.i.g. good yields ofpolyethylene and polypropylene result in a matter of minutes.

By carefully controlling the operating conditions, polymers may beproduced having a wide range of molecular weights. Under the preferredconditions, viz., low tem perature and low pressure, the polymerizationusing the initiator of this invention gives products averaging about30,000 molecular weight or greater. Products much higher, such as100,000, are also produced. Such polymers have softening pointsgenerally in excess of 120 C. (Vicat) and are substantially more rigidthan polymers produced by conventional commercial high pressureprocesses. The polymers are free of zinc and contain only occasionalinsignificant traces of titanium.

The following example is added to illustrate working embodiments of theinvention, it being understood that the invention is not to be therebylimited to this example.

Example Diphenylmercury (0.1 mole) and zinc dust (0.15 mole) are placedin a flask with 200 ml. of decalin and the mixture refluxed six days toform diphenylzinc. At the end of this time the mixture is filtered andthe brown filtrate allowed to cool further. The material left on thefilter is largely amalgamated zinc. On cooling, a cream colored solidslowly precipitated. When this solid settles, the clear brownsupernatant liquid is decanted. It contains a maximum of .005 mole ofdiphenylzinc in ml. of solution.

20 m1. of the solution is then added to 300 ml. of hexane containing1.00 ml. (.009 mole) of titanium tetrachloride. A copious brownprecipitate immediately.

The diphenylzinc-titanium tetrachloride initiator prepared as above isthen placed, as a slurry, in a Parr autoclave at 25 C. and ethyleneadded at 50 p.s.i.g. to the agitated mixture. The temperature need notbe controlled and may rise to 60-70 C. After the uptake of ethylene iscompleted as shown by a steady pressure, the autoclave is opened and themixture filtered to recover polyethylene. It has a softening point of129 C. and a molecular weight (Vicat) of 81,000.

Various changes and modifications of the invention can be made and tothe extent that such variations incorporate the spirit of thisinvention, they are intended to be included within the scope of theappended claims.

What is claimed is:

1. A polymerization initiator formed by reacting a ratio of about onemole of diphenylzinc to about 0.25 to 4 moles of titanium tetrachloridein an inert medium.

2. A polymerization initiator formed by reacting a ratio of about onemole of diphenylzinc to about 0.25 to 4 moles of titanium tetrachloridein the presence of an inert organic solvent.

3. The process which comprises reacting a ratio of about 1 mole ofdiphenylzinc to 0.25 to 4 moles of titanium tetrachloride in thepresence of an inert organic solvent to produce a reaction product.

4. The process which comprises contacting a l-olefin of less than 4carbons with a polymerization initiator consisting essentially of thereaction product of a ratio of about one mole of diphenylzinc to 0.25 to4 moles of titanium tetrachloride in the presence of an inert medium ata temperature from 0 C. to 300 C. and a pressure from atmospheric to2000 atmospheres to produce a polymer of the l-olefin.

5. The process that comprises contacting a l-olefin of less than 4carbons with a polymerization initiator consisting essentially of thereaction product of a ratio of about one mole of diphenylzinc to 0.25 to4 moles of titanium tetrachloride in the presence of an inert organicsolvent at a temperature from 0 C. to C. and a pressure from atmosphericto 1000 p.s.i.g. to produce a polymer of the l-olefin.

6. The process that comprises contacting a l-olefin of less than 4carbons with polymerization initiator consisting essentially of thereaction product of a ratio of about one mole of diphenylzinc to 0.25 to4 moles of titanium tetrachloride in the presence of an inert organicsolvent at a temperature from 0 C. to 100 C. and a pressure fromatmospheric to 200 p.s.i.g. to produce a polymer of the l-olefin.

appears References Cited in the file of this patent UNITED STATESPATENTS OTHER REFERENCES Gilman et al.: J. Organic Chem., (November1945).

4. THE PROCESS WHICH COMPRISES CONTACTING A 1-OLEFIN OF LESS THAN 4CARBONS WITH A POLYMERIZATION INITIATOR CONSISTING ESSENTIALLY OF THEREACTION PRODUCT OF A RATIO OF ABOUT ONE MOLE OF DIPHENYLZINC TO 0.25 TO4 MOLES OF TITANIUM TETRACHLORIDE IN THE PRESENCE OF AN INERT MEDIUM ATA TEMPERATURE FROM 0%C. TO 300*C. AND A PRESSURE FROM ATMOSPHERIC TO2000 ATMOSPHERES TO PRODUCE A POLYMER OF THE 1-OLEFIN.